In a communication apparatus, a plurality of transmitters are used in order to provide directionality to signal radiation characteristics. In this case, the phase difference between the signals output from the respective transmitters is adjusted according to the signal radiation direction. Similarly, in order to provide directionality to signal receive characteristics, the phase difference of received signals is adjusted between a plurality of receivers according to the signal receive direction. When adjusting the phase difference of the signals between the transmitters or receivers, if there are variations among circuit devices such as amplifiers contained in the respective transmitters or receivers, the desired phase difference may not be obtained. In particular, as is the case with signals at millimeter wavelengths, as the wavelength becomes shorter, even a slight shift from the amount of signal delay corresponding to the desired phase difference can result in a larger phase difference error. In view of this, adjusting the phase difference between transmitters by comparing the signals output from the respective transmitters has been proposed (for example, refer to Japanese Laid-open Patent Publication No. 2013-34129).
Japanese Laid-open Patent Publication No. 2013-34129 discloses an inter-branch correction device for a phased-array antenna including a plurality of branches each of which delays the phase of a modulated RF signal and converts the resulting signal into a high-frequency signal for output. This device determines the amount of phase delay in each branch based on the DC component of the output signal obtained by inputting two high-frequency signals output from two adjacent branches into a mixer, and delays the modulated RF signal in one or the other of the branches by the determined amount of phase delay.